The cliffs have great symbolic value in Britain because they face towards continental Europe across the narrowest part of the English Channel, where invasions have historically threatened and against which the cliffs form a symbolic guard. The National Trust calls the cliffs "an icon of Britain", with "the white chalk face a symbol of home and war time defence."[4] Because crossing at Dover was the primary route to the continent before the advent of air travel, the white line of cliffs also formed the first or last sight of Britain for travellers. In World War II, thousands of allied troops on the little ships in the Dunkirk evacuation saw the welcoming sight of the cliffs.[5] During the summer of 1940, reporters gathered at Shakespeare Cliff to watch aerial dogfights between German and British aircraft during the Battle of Britain.[6]l

The white cliffs of Dover seen across the channel from Cap Gris Nez, France. The layers of flint embedded in the chalk match on both sides, showing that in prehistoric times a land connection existed between England and France

Around seventy million years ago Great Britain and much of Europe was submerged under a great sea. The sea bottom was made of a white mud formed from fragments of coccoliths, the skeletons of tiny algae which floated in the surface waters of the sea and then sank to the bottom during the Cretaceous period and together with the remains of bottom-living creatures, formed muddy sediments. It is thought that the sediments were deposited very slowly, probably only half a millimetre a year, equivalent to about 180 coccoliths piled one on top of another. Still, up to 500 metres of sediments were deposited in some areas.[9] Through the weight of overlying sediments, the deposits eventually became consolidated into chalk.[10]

Cliffs, showing multiple layers of flint

Later earth movements related to the formation of the Alps raised these former sea-floor deposits above sea level and until the end of the last glacial period the British Isles were part of continental Europe, linked by the unbroken Weald-Artois Anticline, a ridge that acted as a natural dam holding back a large freshwater pro-glacial lake, now submerged under the North Sea. The two land masses remained connected until between 450,000 and 180,000 years ago when at least two catastrophic glacial lake outburst floods breached the anticline destroying the ridge that connected Britain to Europe, although a land connection across the southern North Sea would have existed intermittently at later times when periods of glaciation resulted in lowering of sea levels.[11] At the end of the last glacial period around 10,000 years ago, rising sea levels finally severed the last land connection.[12]

Evidence of erosion along the cliff top

The above photo of the face of the cliffs shows horizontal bands of dark-coloured flint in the chalk deposits of the cliffs. The flint is composed of the remains of sea sponges and siliceous planktonic micro-organisms which hardened into the microscopic quartz crystals which constitute flint. The quartz silica also filled cavities left by dead marine creatures which are now found as flint fossils, especially the internal moulds of Micraster echinoids. Several different ocean floor species such as brachiopods, bivalves, crinoids, sponges and others, as well as shark teeth can also be found in the chalk deposits.[13]

In some areas layers of a soft, grey chalk known as a hardground complex can be seen. Hardgrounds are thought to reflect disruptions in the steady accumulation of sediment during which times sedimentation ceased and/or the loose surface sediments were stripped away by currents or slumping, exposing the older hardened chalk sediment. A single hardground may have been exhumed 16 or more times before the sediments were compacted and hardened (lithified) to form chalk.[14]

The cliff face continues to weather at an average rate of 1 centimetre (0.4 in) per year, although occasionally large pieces will fall. This occurred in 2001, when a large chunk of the edge, as large as a football pitch, fell into the Channel.[15] A further large section collapsed into the Channel on 15 March 2012.[16] Visitors are, therefore, urged to remain well away from the cliff edge.

The chalk grassland environment on the land surface above the cliffs provides an excellent environment for many species of wild flowers, butterflies and birds and has been designated a Special Area of Conservation and a Site of Special Scientific Interest. Rangers and volunteers work to clear invasive plants that threaten to invade the native flora. A grazing programme involving Exmoor ponies has been established to help to clear out the faster-growing invasive plants, allowing smaller, less robust native plants to survive. [17] These hardy ponies have been managed by organisations such as the National Trust, Natural England, and County Wildlife Trusts to maintain vegetation on nature reserves. [18]

Horseshoe Vetch, the sole food for the Adonis blue butterfly

Chalk Hill Blue, male

Chalk Hill Blue, female

Among the wildflowers on the cliffs there is a surprising variety of orchids, the most nationally rare being the Early Spider Orchid with yellow-green to brownish green petals and a flower that looks like the body of a large spider. Similar in appearance but from a different family is the Oxtongue Broomrape with yellow, white, or blue snapdragon-like flowers. The cliffs are home to 90 percent of the UKs population of Oxtongue broomrape, an unusual plant in that it lives on the roots of a host plant. Viper's-bugloss, a showy plant in vivid shades of blue and purple with red stamens, also grows along the cliffs.[19] In King Lear Shakespeare mentions an edible plant, rock samphire, that grows on the cliffs and was once collected by gatherers hanging down on ropes: Half-way down Hangs one that gathers samphire; dreadful trade! (Act IV, Scene VI). This refers to the dangers involved in collecting rock samphire on sea cliffs.

The abundance of wildflowers provides a home for around 30 different species of butterflies. A rare butterfly, the Adonis blue, can be seen in spring and again in the fall. Males have vibrant blue wings which are lined with a white margin, whereas the females are a rich chocolate brown. This species needs the plant Horseshoe Vetch and a certain kind of red ant to survive. It overwinters as a green and yellow-striped caterpillar, a coloring which camouflages it while it feeds on vetch. When it is ready to pupate, it searches for ants to 'milk' its sugary secretions. In April-May and July-August the caterpillar forms into a chrysalis in a small crevice and it is then buried by the ants in chambers connected to their nest. The ants then care for it for around three weeks, protecting it from predators until it is ready to emerge as a butterfly.[20] Similar in appearance but more abundant is the Chalk Hill Blue. It is a specialist to chalk grassland and can be seen in July and August.[21][22] Threatened species include the Silver Spotted Skipper and Straw Belle Moth. The well known Red Admiral can be seen from February through November. The Marbled white, black and white with a white wing border, can be seen from June to August.

Peregrine off White Cliffs, Dover

The cliffs are popular for many migratory birds, being the first landing point for species flying inland from the English Channel. After a 120-year absence, in 2009 it was reported that ravens had returned to the cliffs. Similar in appearance but smaller, the jackdaw is abundant. The rarest of birds that live along the cliff is the peregrine falcon. They can reach a hunting dive of 200mph, the fastest animal in the world. In recent decline and endangered, the skylark also makes its home on the cliffs.[23] The cliffs are also home to the fulmar which resemble gulls and colonies of black-legged kittiwake a species of gulls. Although the well known wartime song "(There'll Be Bluebirds Over) The White Cliffs of Dover" mentions bluebirds flying over the cliffs of Dover, bluebirds are an American species that do not make their home in Europe. However, bluebird is an old country name for swallows and house martins which do make an annual migration to the continent, with many crossing the channel at least twice a year and spending the summer in the vicinity of Dover.

Dover Castle is a medieval castle founded in the 11th century and has been described as the "Key to England" due to its defensive significance throughout history.[24][25] It is the largest castle in England.[26]

Samphire Hoe Country Park is a nature reserve situated on a new piece of land created by the earth excavated during the construction of the Channel Tunnel. It covers a 30-hectare site at the foot Shakespeare Cliff, between Dover and Folkestone. There is an education shelter with a classroom and exhibition area. Staff and volunteers are available to answer questions and provide information about the wildlife in the reserve. The building's design incorporates eco-construction criteria.

Dover Museum was founded in 1836. Shelled from France in 1942 during the Second World War, the Museum lost much of its collections, including nearly all of its natural history collections. Much of the surviving material was left neglected in caves and other stores until 1946. In 1948 a 'temporary' museum was opened and in 1991 a new museum building of three stories (built behind the Museum's original Victorian facade) was opened. In 1999, a new gallery on the Museum's second floor centred on the Dover Bronze Age Boat was opened.[27]

Vera Lynn, known as "The Forces Sweetheart" for her 1942 wartime classic "(There'll Be Bluebirds Over) The White Cliffs of Dover", celebrated her 100th birthday in 2017. That year she led a campaign for donations to buy 700,000 sqm of land atop Dover's cliffs when it was feared that they may be sold to developers. The campaign met its target after only three weeks. The National Trust, which owns the surrounding areas, plans to return the land to a natural state of chalk grassland and preserve existing military structures from World War II.[28]

In 1867, English poet Matthew Arnold wrote the poem Dover Beach eptimising the beauty of the Kent coast.

The most famous reference in English literature to the White Cliffs is in Shakespeare's King Lear, Act IV, Scene I. Edgar persuades the blinded Earl of Gloucester that he is at the edge of a cliff in Dover. Gloucester says "There is cliff, whose high and bending head looks fearfully in the confined deep: Bring me to the very brim of it." Edgar fools the Gloucester into thinking he is at the cliff edge and describes the scene: "Here's the place! - stand still - how fearful/ And dizzy 'tis, to cast one's eye so low [...] half way down/Hangs one that gathers samphire: dreadful trade!/Methinks he seems no bigger than his head."[30]

Samphire is a wild edible plant that grew on the cliffs and was gathered by hanging from ropes over the cliff's edge at that time. "Shakespeare Cliff" was named after the reference.

^Cathcart King, David J. (1983). Catellarium Anglicanum: An Index and Bibliography of the Castles in England, Wales and the Islands. Volume I: Anglesey–Montgomery. Kraus International Publications. p. 230.